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This article covers five of the most commonly requested blood tests in primary care, and what they mean for patients.

Reflect

What would a gamma-glutaryl transferase test indicate? What would be measured in a whole blood count? What is alanine aminotransferase?

Plan

This article will help you understand why certain blood tests are carried out, what the results might indicate and the range of values considered ‘normal’ for these tests.

Act

• Review the diagnostic tests you carry out either in your pharmacy or sell for home testing. Are you sure exactly how they are used and the advice you should give to users? Do you have trained staff to advise on these tests when you are busy doing something else? Should you extend the range of tests you offer?

• Read the Diagnostics section in the C+D Guide to OTC Medicines and Diagnostics to see what blood pressure and blood glucose monitors are available for sale through pharmacies. Read the fertility tests section, in particular the counselling points.

• Find out which drugs and factors other than diet are likely to increase cholesterol levels. How long after a bout of flu should someone wait before having their cholesterol measured? How does pregnancy affect cholesterol levels? The answers to these questions can be found on www.labtestsonline.org.uk .

• Look up the following on the above website, in particular the sections giving more information about the tests and the questions commonly asked about them: ALT, bilirubin, creatinine, GGT, haemoglobin, potassium, sodium, red and white blood counts, and urea. Look at the links to the diseases that the tests monitor or detect.

• When should you refer customers taking OTC simvastatin for a liver function test? Revise the Royal Pharmaceutical Society’s practice guidance on this drug and the Bandolier opinion on statins and the liver at the Healthy Living Zone.

Evaluate

• Would you now be able to interpret blood test results if a patient asked you for help? What else might you do to improve the diagnostic testing services you offer?

A regular customer comes into the pharmacy holding the results of a blood test from a screening initiative at a ‘well man’ clinic.

He asks if you can explain what the following test results mean: TSH, ALT, gamma GT, potassium/sodium, urea, creatinine, haemoglobin, and WBC.

This article will be useful when patients bring blood test results into pharmacies seeking an opinion, and also for anyone planning a service that involves screening bloods.

There is a growing recognition from the government that community pharmacy is an untapped resource, and has an important role to play in requesting, interpreting and advising on such tests.

The reference range

A blood test result will either be positive or negative. A cut-off point at either end of a normal distribution curve for 95 per cent of a healthy population is used to distinguish between these results. These two cut-off points make up the reference range for a particular test. Reference ranges may vary slightly depending on the laboratory used to generate the results.

Commonly requested blood tests

Blood tests are among the most commonly performed medical tests. As a community pharmacist you are likely to see patients with request forms from GP practices for the following types:

• full blood count – red blood cells (RBCs), white blood cells (WBCs) and platelets

• blood chemistry – urea and electrolytes (Us and Es)

• kidney function tests

• liver function tests (LFTs)

• hormone levels, eg thyroid levels

• blood glucose level

• blood clotting tests – international normalized ratio (INR)

• tests for inflammation, eg erythrocyte sedimentation rate (ESR)

• therapeutic drug monitoring, eg digoxin, lithium, theophylline

• immunology – checking for antibodies to certain viruses and bacteria

• blood grouping

Another common test is blood cholesterol, but this is too large a topic for this article.

Full blood count (FBC)

What is tested?

This test is one of the most common and looks at the levels of erythrocytes (RBCs), leucocytes (WBCs) and thrombocytes (platelets). There are five types of leucocyte: neutrophils, eosinophils, basophils, lymphocytes and monocytes.

This test:

• counts the number of RBCs, WBCs, and platelets per ml of blood

• measures the size of the RBCs and calculates their average size

• calculates the proportion of blood made up from RBCs (the haematocrit or packed cell volume (PCV))

• measures the amount of haemoglobin in the RBCs. The mean cell haemoglobin concentration (MCHC) is a measure of

the average concentration of haemoglobin.

Reference values

Red cell count (RCC) 4.5-6.5 x 102/l (men)

3.9-5.6 x 1012/l (women)

MCHC 30-36 g/dl

PCV 0.4-0.54 (men)

0.37-0.49 (women)

Haemoglobin 13.5-17.5 g/dl (men)

11.5-15.5 g/dl (women)

WCC 4.0-11.0 x109/l

Platelet count 150-400 x109/l

Ferritin 24-300ng/L (men)

15-300ng/L (women)

Serum iron 10-30emol/l

Total iron binding capacity (TIBC)

40-75emol/l

What does it mean?

Abnormalities that can be detected include:

• Anaemia where the RCC is lower than normal. In this situation there is less haemoglobin than normal in each RBC, or the RBCs are smaller than normal.

If a blood count indicates that the haemoglobin and haematocrit are low, especially if the RBCs are smaller than normal, this indicates an anaemia due to iron deficiency. Ferritin and other iron tests (usually a serum iron test and the TIBC) can then be requested to confirm the diagnosis.

In healthy people, most iron is stored in the protein ferritin, which is present mostly in the liver, but also in the bone marrow, spleen, and muscles. Small amounts of ferritin also circulate in the blood, therefore the amount of ferritin in the blood reflects the amount of iron stored. TIBC measures the amount of transferrin, a blood protein that transports iron from the gut. The body makes transferrin in relationship to the need for iron; when iron stores are low, transferrin levels increase, while transferrin is low when there is too much iron.

An iron test is usually taken in the morning before the patient has anything to eat (ie a fasting blood test). If patients are already taking iron tablets then they should be told to avoid taking the tablets for 24 hours before the test.

• Leucopenia (too few WBCs). Depending on which WBC level is reduced, this may be neutropenia, lymphopenia, or eosinopenia. The term agranulocytosis applies if there is pronounced leucopenia and is potentially fatal. The condition is characterised by onset of sore throat, bruising or bleeding, mouth ulcers, fever, and malaise. Drugs that can cause leucopenia and agranulocytosis include methotrexate, carbimazole and carbamazepine.

• Leucocytosis (too many WBCs). Depending on which type of WBC is increased, it is called neutrophilia, lymphocytosis, eosinophilia, monocytosis, or basophilia. There are various causes, eg infections can cause a WBC increase, while leukaemia causes a large increase in the number of WBCs. The type of leukaemia depends on the type of WBC affected.

• Thrombocytopenia (too few platelets). This may make patients bruise or bleed easily. Drugs such as carbamazepine and methotrexate can cause this condition.

Tests for inflammation

What is tested?

If there is inflammation in the body, extra protein is often released from the site and circulates in the bloodstream.

The ESR blood test is commonly used to detect this increase in protein, so is a ‘marker’ of inflammation. The ESR test literally measures the rate at which the RBCs separate from the plasma and fall to the bottom of a test tube. If inflammatory proteins attach to the RBCs, the RBCs will ‘sediment’ more quickly. A high ESR indicates that inflammation is present.

Reference values

Erythrocyte sedimentation rate (ESR):

• <10 mm/hr (men)

• <20 mm/hr (women)

What does it mean?

The ESR is a ‘non-specific’ test – a raised level means inflammation is present, but further tests will be needed to clarify the cause. The ESR level is raised in many inflammatory conditions, including bacterial infections, rheumatoid arthritis, Crohn’s disease, organ transplant rejection, and heart attack. Changes in ESR are also used to monitor responses to treatment in conditions such as rheumatoid arthritis.

Liver function tests (LFTs)

What is tested?

The by-products of liver metabolism circulate in the bloodstream and bile. Common LFTs are:

• Alanine aminotransferase (ALT)This enzyme metabolises protein in the liver. When the liver is injured or inflamed (as in hepatitis), the ALT blood level usually rises.

• Alkaline phosphatase (ALP) This enzyme occurs mainly in the liver and in bone, therefore the blood level is raised in some types of liver and bone disease.

• Gamma-glutamyl transferase (GGT) This enzyme is present in high concentrations in the liver, and levels become raised in all types of liver and biliary tract disease. This measurement is most useful in patients at risk of liver disease due to alcoholism.

• Albumin This is the main protein made by the liver, and it circulates in the bloodstream. The ability to make albumin (and other proteins) is affected in some types of liver disorder. A low level of blood albumin therefore occurs in some liver disorders, including cirrhosis.

• Total protein This measures albumin and all other proteins in blood.

• Bilirubin This is the chemical that gives bile its yellow/green colour. A high level of bilirubin in blood will make a patient appear jaundiced. Bilirubin is made from haemoglobin, which is released when RBCs break down at the end of their 120-day lifespan. The liver then metabolises this bilirubin to ‘conjugated bilirubin’ which is then passed into the bile ducts.

A raised blood level of conjugated bilirubin occurs in various liver and bile duct conditions. It is particularly high if the flow of bile is blocked, eg by a gallstone in the common bile duct, or a tumour in the pancreas. It can also be raised with hepatitis, liver injury or long-term alcohol abuse.

A raised level of unconjugated bilirubin occurs when there is excessive breakdown of RBCs, as in haemolytic anaemia.

Reference values

Albumin 35-55g/l

Total bilirubin 3-20emol/l

Conjugated bilirubin 0-14emol/l

Alanine aminotransferase (ALT) 0-45iu/l

Alkaline phosphatase (ALP) 90-300iu/l

Gamma-glutamyl transferase (GGT):

0-70iu/l (men)

0-40iu/l (women)

What does it mean?

LFTS are used:

• to help diagnose liver disorders if there are suggestive symptoms, eg jaundice.

• to monitor the activity and severity of liver disorders

• as a routine precaution after starting certain drugs to check they are not causing liver damage as a side effect eg statins.

Patients are usually advised to fast for four to eight hours before blood samples are taken for LFTs.

Kidney function tests

What is tested?

The usual blood test that checks the kidneys are working properly measures the level of urea, creatinine, and certain electrolytes (sodium, potassium, chloride and bicarbonate).

Urea is a waste product formed from the breakdown of proteins, which is passed out in the urine. A high blood level of urea (‘uraemia’) indicates that the kidneys may not be working properly. One measurement of the amount of urea in the blood is called the blood urea nitrogen (BUN) test.

Creatinine is a waste product of muscle metabolism, which is also passed out in urine. Again, high creatinine indicates that the kidneys may not be working properly, and is considered a more accurate marker of kidney function than urea.

Reference values

Sodium 135-148mmol/l

Potassium 3.5-5.0mmol/l

Chloride 95-105mmol/l

Serum creatinine 0.7-1.4mg/dl

Blood urea nitrogen (BUN) 7-20mg/dl

What does it mean?

Routine kidney function is one of the most commonly performed blood tests. It may be done:

• as part of a general health assessment

• if dehydration is suspected (when the urea level increases)

• to test for kidney failure by checking the blood levels of urea and creatinine

• before and after starting certain drugs, such as ACE inhibitors.

Thyroid function tests

What is tested?

Thyroid function tests involve measuring one or both of the following:

• Thyroid-stimulating hormone (TSH). This hormone is synthesised in the pituitary gland and stimulates the thyroid gland to make the thyroid hormones. If the level of thyroid hormones in the blood is high, then the pituitary releases less TSH. Therefore, a low level of TSH means the thyroid gland is overactive (ie hyperthyroidism). Similarly, a high level of TSH means the thyroid gland is underactive.

• Free thyroxine (T4)/tri-iodothyronine (T3). A high level of free T4 and free T3 confirms hyperthyroidism. A low level of free T4 and free T3 confirms hypothyroidism.

Reference values

TSH 0.5-5.5miu/l

Free T4 9.4 -25.0pmol/l

Free T3 3.0-8.6pmol/l

What does it mean?

Both hyper- and hypothyroidism can be differentiated into overt and subclinical:

• Overt hyperthyroidism is diagnosed when the TSH level is suppressed, with free T4 and/or T3 levels above the normal reference range, in a person with symptoms of hyperthyroidism. Overt hypothyroidism is diagnosed on the basis of characteristic clinical features of hypothyroidism, with a serum TSH concentration above the normal reference range and a serum free T4 concentration below the reference range.

• Subclinical hyperthyroidism is diagnosed when the TSH level is suppressed, with free T4 and T3 levels within the normal reference range, in an asymptomatic person. Subclinical hypothyroidism is diagnosed when there are no specific symptoms or signs of thyroid dysfunction but the TSH concentration is above the reference range and the free T4 concentration is in the normal range.

CPD – The College of Pharmacy Practice

This course (module 1442), in association with multiple choice questions being published in C+D July 5, provides one hour’s continuing education

This article can help in the following CPD competencies: G1a, G1b, G1d, G1e, G2o, C1f, C2e.